fix(perf): Optimize calls to `/version` with RequestCache

Description

This MR optimizes how we retrieve the relevant GitLab instance version by:

• Introducing a utility RequestCache
• Introducing a singleton getGitLabVersion that uses RequestCache

How has this been tested?

• Unit tests still pass 👍.
• Manually with Run Extension task and verifying the number of /version calls in the extension logs.

Screenshots (if appropriate)

Before	After

What CHANGELOG entry will this MR create?

• fix: Bug fix fixes - a user-facing issue in production - included in changelog
• feature: New feature - a user-facing change which adds functionality - included in changelog
• BREAKING CHANGE: (fix or feature that would cause existing functionality to change) - should bump major version, mentioned in the changelog
• None - other non-user-facing changes